Looking at the large version speed control appears to be achieved by setting the top air vanes to give the basic speed and the lower vanes appear to be controlled by the weights moving the levers and tilting the vanes.

Fred, Here are three images of the Point Reyes clockwork that more clearly show the vanes, pendulum weights, etc. I believe you are correct that the weights control the lower vanes. Tilting of the vanes would increase or decrease air resistance much like that for propeller blades on a plane----David

For Stevenson design clockwork with endless chain the winding should not interrupt lens rotation.

For the Pt. Reyes clockwork design with a cable with weight wound on the drum---good question.

It appears to me with limited knowledge that this clockwork could not drive the lens during the time interval required to wind the weight. For Pt. Reyes how much time to wind the weight I do not know but not a great amount, the tower being only 35 feet high and half or more of which is the first order lantern.

I know how the Stevensons did it with some of there machines,not applicable in this case.

With the photographs you can work out the speed control,you can see the ratchet mechanism for rewinding,so far I can see part of the gear on the final drive shaft but I can't see the intermediate gear between cable drum and final drive which would give a clue to whether the lens continued to rotate or not?

Not exactly what we are seeking but I found on Google books a really comprehensive book, Lightships and lighthouses by Frederick Arthur Ambrose Talbot, 1913. A lot of detailed descriptions and many historic photos.

on page 43:"In the case of an immense apparatus such as a hyperradiant lens, which, together with the turntable, may have a total weight of 17,000 pounds, an enormous quantity of mercury is required. The trough of the Cape Race hyperradiant light carries 950 pounds of quicksilver, upon which the lantern is floated. In such an instance, also, the pedestal is a weighty part of the apparatus, representing in this case about 26,800 pounds, so that the complete apparatus utilised to throw the 1,100,000 candle-power beam from the guardian of the Newfoundland coast aggregates, when in working order, some 44,000 pounds, or approximately 20 tons.""Within the base of the pedestal is mounted the mechanism for rotating the optical apparatus. This is of the clockwork type driven by a weight. The latter moves up and down a tube which extends vertically to a certain depth through the centre of the tower. The weight of the driving force and the depth of its fall naturally vary according to the character of the light. In the Cape Race light the weight is of 900 pounds, and it falls 14.5 feet per hour. Similarly, the length of time which the clock will run on one winding fluctuates. As a rule it requires to be rewound once every sixty or ninety minutes. A longer run is not recommended, as it would demand a longer weight-tube, while many authorities prefer the frequent winding, as the man on duty is kept on the alert thereby. As the weight approaches the bottom of its tube it sets an electric bell or gong in action, which serves to warn the light-keeper that the mechanism demands rewinding."________________This light displayed a white flash every 7.5 seconds. With four bulls-eyes four flashes each 30 seconds, this lens was revolving at 2 rpm. For a 14.5 foot weight drop per hour, -- 8.28 revolutions per foot weight drop.

From the Point Reyes historic resource study written by the park historian about thehistory and architecture of the Point Reyes Light Station -- the clock does not drive the apparatus when being rewound.

Clockwork timing and thus rotation of the lens is adjusted by changing the angle of inclination of the two clockwork "wings" and if necessary adding or removing weight.